Cephalodiscida is one of two orders in the class

Pterobranchia Pterobranchia, members of which are often called pterobranchs, is a class of small worm-shaped animals. They belong to the Hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water w ...

, which are small, worm-shaped animals. Members belong to the

hemichordates Hemichordata ( ) is a phylum which consists of triploblastic, eucoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and includ ...

. Species in this order are

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

, living in clear water and

secrete Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mec ...

tubes on the

ocean floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

Taxonomy

The order is a small one, with only two known families, each containing a single extant genus. The validity of the family Atubaridae, who has only a sole member, is regarded as questionable. * Order Cephalodiscida Fowler 1892 ** Family

Cephalodiscidae ''Cephalodiscus'' is a genus of hemichordates in the monotypic family Cephalodiscidae of the order Cephalodiscida. Description All known species live in a secreted coenecium attached to a rock substrate. Unlike ''Rhabdopleura'', ''Cephalodisc ...

Harmer 1905 *** Genus †'' Aellograptus'' Obut 1964 *** Genus †'' Eocephalodiscus'' Kozlowski 1938 ex Kozlowski 1949 *** Genus †'' Melanostrophus'' Öpik 1930 ex Öpik 1933 *** Genus †'' Pterobranchites'' Kozlowski 1967 *** Genus ''

Atubaria ''Atubaria heterolopha'' is a species of hemichordates in the monotypic genus ''Atubaria'' and in the monotypic family Atubaridae. This taxon belongs to the pterobranchian order Cephalodiscida. It was described by Tadao Sato in 1936 from specimen ...

'' Sato 1936 *** Genus ''

Cephalodiscus ''Cephalodiscus'' is a genus of hemichordates in the monotypic family Cephalodiscidae of the order Cephalodiscida. Description All known species live in a secreted coenecium attached to a rock substrate. Unlike ''Rhabdopleura'', ''Cephalodiscu ...

'' M'Intosh 1882 ** Family †

Rotaciurcidae ''Rotaciurca'' is an extinct genus of Silurian cephalodiscid pterobranchs. The genus contains a single species, ''Rotaciurca superbus'', known from the Bertie Group of Ontario, Canada. Description ''Rotaciurca'' is a pseudocolonial (contain ...

Briggs and Koch 2023 *** Genus †''

Rotaciurca ''Rotaciurca'' is an extinct genus of Silurian cephalodiscid pterobranchs. The genus contains a single species, ''Rotaciurca superbus'', known from the Bertie Group of Ontario, Canada. Description ''Rotaciurca'' is a pseudocolonial (contain ...

'' Briggs and Koch 2023

References

Harmer. S. F. 1905. The Pterobranchia ol the Siboga-Expedition. Siboga Exped. Monogr. 26. 1-131 Pterobranchia Bilaterian orders {{hemichordate-stub